1. Field of the Invention
The present invention relates to image-signal processing devices and image-signal processing programs.
2. Description of Related Art
Noise components that are included in digitized signals obtained from an image capturing element and an analog circuit and an A/D converter used in combination with the image capturing element can be broadly classified into fixed-pattern noise and random noise. The fixed-pattern noise is noise caused mainly by the image capturing element, such as defective pixels. The random noise is generated at the image capturing element and the analog circuit and has characteristics similar to white noise characteristics.
For example, Japanese Unexamined Patent Application, Publication No. 2001-157057 discloses a method in which the noise level is represented as a function of the signal level, the noise level associated with the signal level is estimated with the function, and frequency characteristics for filtering are controlled on the basis of the estimated noise level, thereby reducing random noise.
In the invention of Japanese Unexamined Patent Application, Publication No. 2001-157057, the noise level N is represented by the following function.N=a·bc·D  (1)
In equation (1) above, N is the noise level, a and b are arbitrary positive real numbers, c is an arbitrary negative real number, and D is the intensity signal value, and these values are given statically.